My local Sainsbury`s have just introduced them. I`ve used them 4 times and had problems twice so 50% isn`t very good. I got a feedback form from customer services. Their problem seemed to be that when there was an offer such as 2 for 1 you couldn`t tell if you had got the discount until you had paid and got the receipt. Low and behold, the discount hadn`t gone through and I had to go to customer services. Would be useless for someone like my Mum as well who is elderly and can`t see! They`re Ok as long as they don`t take over which they will probably do as they are cheap and all supermarkets think about is profit